For many women of child-bearing age, oral contraceptive use is as routine as taking a daily multivitamin is for others. Though various forms of contraceptives are available and used, oral birth control remains the most prevalent form of contraception among women. Most often, patient education focuses on the benefits of oral contraception including convenience and effectiveness, but may not give a comprehensive understanding of the risks, contraindications, or interactions with food and nutrients. Nutrient interactions are especially important for women of child-bearing years and yet, very few are aware that their birth control pills may be depleting their body of critical nutrients needed for optimal cognition, mood, cardiovascular health, and should they choose to become pregnant, the health of their unborn child.

Oral contraceptives that contain a mixture of estrogen and progestin may increase the risk of deficiencies in vitamins B6, B12, and folate – three critical nutrients for health and wellness in women of child-bearing age. These vitamins play roles in methylation, DNA synthesis, and neurological function. Depletion is often associated with anemia, depression, and poor cognitive function. Not only do these micronutrients function in independent roles, but many more functions require them to work collectively, meaning a deficiency in one can alter the functional ability of the other two.

So how impactful are oral contraceptives on vitamin status?

Vitamin B12

In a randomized controlled trial of healthy active women, blood samples were collected every 4 weeks at 3 intervals and serum was analyzed for folate, B12, and B6 concentrations. Erythrocyte folate was also determined. The subjects did not take any other medications. BMI, age, physical activity, and alcohol intake was accounted for and food frequency questionnaires were completed to determine the dietary intake of the micronutrients. Among all the micronutrients analyzed, users of oral contraceptives showed significantly lower vitamin B12 concentrations in all measurements not explained by a lack of dietary intake or lifestyle factors.

Folate

In a systematic review and meta-analysis seeking to determine the association between folate status and oral contraceptive use, a significant folate-lowering effect of oral contraceptives was noted among the 2831 women analyzed in 17 studies. These results were further supported by data from an additional 1389 women in 12 studies whose RBC folate concentrations were significantly lower among users of oral contraceptives.

Since adequate folate is crucial for neurological development of the embryo and fetus in the first few weeks following conception (a time in which the women often does not know she is pregnant), this nutrient deficiency poses a severe threat to women previously taking oral contraceptives, but then discontinuing them just prior to conception, and especially to those who may become pregnant despite birth control. Therefore, folate-fortified oral contraceptives were introduced to address this problem. A systematic review evaluating the effectiveness of this option in achieving and maintaining healthy folate concentrations (determined by the recommended minimum concentration necessary to prevent neural tube defects) found that folate-fortified oral contraceptives were at least as effective as folic acid supplementation for raising blood folate levels.

Vitamin B6

Oral contraceptives are also associated with low plasma pyridoxal 5′-phosphate (the coenzyme form of vitamin B6). A study of 157 healthy women using either combined estrogen and progestin or single hormone oral contraceptives for more than 6 months investigated the association between vitamin B6 metabolites (rather than just vitamin B6 concentration) and oral contraceptives. The study only included women who also had normal total homocysteine concentration, no history of gastrointestinal surgery, abnormal kidney or thyroid function, or any other chronic disease; no smoking or chronic drug use or alcoholism; BMI <28 kg/m²; no vitamin, amino acid, or protein supplementation; no chronic consumption of a high-protein diet; not pregnant and with adequate nutritional status. Since vitamin B6 is a coenzyme in various metabolic processes, measuring the metabolites can give a better indication of the potential physiological impact of oral contraceptives as it relates to vitamin B6. Several metabolites were measures and overall, it was found that oral contraceptives have effects on metabolites and ratios of one-carbon metabolism and tryptophan catabolism, which could explain some of the known adverse outcomes of hormonal birth control such as shifts in carbohydrate and fat metabolism, and cardiovascular risk factors.

Since oral contraceptive use is so prevalent among women of child-bearing years, it is important to educate them on the possible effects of these drugs on nutritional status and provide them with options for maintaining adequate levels of micronutrients. Although other micronutrient deficiencies have been associated with the use of oral birth control, vitamins B12 and B6, and folate are three of the most important nutrients to address considering their impact on the health of both the woman and any future children she may bear.